Single wall domain arrangement

ABSTRACT

Spurious single wall domains, periodically introduced into the vicinity of an operating single wall domain circuit particularly during high speed operation, are eliminated by a propagation annulus encompassing the circuit. The annular is operative to move domains in a direction outwardly across its axis.

United States Patent 1 11 1 1 ,726

Bobeck 1 Apr. 24, 1973 1 SINGLE WALL DOMAIN 3,641,518 2/1972 Copeland..340/|74 TF ARRANGEMENT OTHER PUBLlCATlQNS [75] lnvemor' :T HenryBobeck Chatham IBM Technical Disclosure Bulletin, Vol. 14, No. 6,

Nov. 1971.1 2. l806-l807 [73] Assignee: Bell Telephone Laboratories,lncor- IBM Technical Disclosure Bulletin, Vol. 15, N0. 2,

porated, Murray Hill, NJ. July 1972, pg. 529 [22] Filed: 1972 PrimaryExaminer.lan1es W. Mofi'itt [21] Appl. No; 228,199 Attorney-R. J.Guenther et al.

' [57] ABSTRACT [52] U.S. Cl. ..340/174 TF, 340/174 SR 51 Int. Cl ..c1111/14, 61 1c 19/00 Spurious Single wall domains. periodically introduced[58] Field of Search ..340/ l 74 TF into the vicinity of n Operatingsingle wall domain circult particularly during high speed operation, arel 56] References Cited eliminated by a propagation annulus encompassingthe circuit. The annular is operative to move domains in a UNITED STATESPATENTS direction outwardly across its axis. 3,676,872 7/1972 Lock..340/ 174 TF 11 Claims, 3 Drawing Figures I MINOR LOOP MAJOR LOOP i 'glC I 22 23 2O 1 s 2 BIAS CONTROL ROTATING FIELD SOURCE CIRCUIT FIELDSOURCE Patented April 24, 1973 ROTATING FIELD SOURCE CONTROL CIRCUITBIAS FIELD SOURCE IAA M I LA? I I...

Ag I SINGLE WALL DOMAIN ARRANGEMENT FIELD OF THE INVENTION BACKGROUND OFTHE INVENTION A. H. Bobeck, U.S. Pat. No. 3,534,347 issued Oct. 13, 1970describes an arrangement for moving single wall domains in a layer ofmaterial along multistage propagation channels defined by a pattern ofmagnetically soft elements in response to a magnetic field reorientingin the plane of the layer. Propagation of domains in the mannerdescribed in that pattern has become known as a field-access mode ofpropagation because the rotating field provides the driving force fordomain movement.

Copending application Ser. No. 160,841 filed July 8, 1971 for A. H.Bobeck and H. E. D. Scovil describes a fine-grained pattern ofmagnetically soft elements which not only defines multistage propagationchannels for domains but permits lateral displacement of domains fromone channel to another as well as certain logic functions. The termfine-grained herein means that adjacent elements of a stage of a channelare spaced apart distances about equal to or less than the diameter ofadomain moved by the pattern.

The fabrication of any single wall domain arrangement necessitatescertain mechanical operations which result in the introduction ofspurious domains into the vicinity of operative domain channels. Forexample, domains are moved in a layer of epitaxially grown materialwhich is diced into areas sufficiently large to accommodate thechannel-defining patterns. The dicing procedure results in abraded edgeswhich give rise to suprious domains during later operation. Moreover,

the pattern of magnetically soft material which defines the domainpropagation channels in the field-access arrangement is formed byphotolithographic techniques which typically employ alignment patternswhich give rise to spurious domains. Both circuit and crystal defectsalso give rise to spurious domains as is well known. Particularly duringthe testing of finished domain circuits to establish margin limits aresuch spurious domains introduced. But even in this situation, thedomains have only negligible effect on circuit operation at quasistatic(low frequency) speeds.

At high speeds (in excess of I kc) on the other hand, the situation isquite different. Even infrequent introduction of spurious domains,particularly when added to others introduced during testing, results inthe presence of a considerable number of domains in relatively shortorder. If it is recalled that single wall domains repel one another, itmay be appreciated that increasingly larger numbers of domainsdistribute themselves within the available space in an array whicheventually encroaches on the operative circuit. When the domain pressurebecomes sufficiently high, interaction between data representing domainsand spurious domains results in random nonrecurring failures.

The problem then is how to prevent the movement of domains from the edgeof the domain layer into the vicinity of the operative circuit and,further, how to eliminate spurious domains which are generated in thevicinity of the operative circuit. The problem is compounded by therealization that any implementation which functions in the sense of afamiliar guard rail may be operative itself to generate spurious domainsand is ineffective in eliminating domains within its confines.

BRIEF DESCRIPTION OF THE INVENTION The invention is based on therecognition that a single wall domain circuit operative in thefield-access mode may be encompassed by a propagation annulus comprisingillustratively a fine-grained pattern of magnetically soft elementsoperative, in response to the already present inplane field, to movespurious domains along radial paths outwardly from the vicinity of theoperative circuit. The annulus is effective not only in excludingspurious domains generated, for example, at the edges of the domainlayer but also in removing from within its confines any spurious domainswhich might be created due to alignment patterns or crystal or circuitdefects in, for example, the event of a temporary loss of power.

It is to be remembered that it is most likely that an occasionalspurious domain will have only a negligible disrupting influence on anoperative circuit as has been indicated above and that a considerablenumber of domains would be necessary to build up a domain pressureresulting in disruptive interactions. A propagation annulus inaccordance with one aspect of this invention relieves this pressureallowing domain movement only outwardly through it into a nonoperativeportion of a domain layer.

In one specific embodiment of this invention, a propagation annulus isdefined by three concentric circles of elements arranged in .a closedloop chevron pattern with the apices of the elements directed along theloop axis. In response to a counterclockwise rotating in-plane field,spurious domains are moved outwardly from an operative circuitencompassed within the closed loop.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation ofa single wall domain arrangement including a propagation ring or annulusin accordance with this invention; and

FIGS. 2 and 3 are schematic representations of portions of thearrangement of FIG. 1.

DETAILED DESCRIPTION FIG. 1 shows a domain propagation arrangement 10 inaccordance with this invention. The arrangement comprises a layer 11 ofa magnetic material in which single wall domains can be moved. A patternof magnetically soft elements is formed by familiar photolithographictechniques for defining domain propagation channels. The illustrativepattern is shown in line diagram form as a major-minor memoryorganization disclosed in U.S. Pat. No. 3,618,054 of P. I. Bonyhard-U.F. GianolaA. J. Perneski. The major-minor memory organization as well asits implementation and operation is now well known in the art. What isimportant here is that an operative organization, illustrativelyimplemented in the field-access mode is encompassed by a propagationring 12 in accordance with this invention for the removal of spuriousdomains.

FIG. 2 shows a portion 13 of ring 12 to include a finegrained pattern ofchevron elements. These elements are formed by the same process whichforms the channel-defining elements of the major-minor organization whenthe photographic mask which defines the pattern is suitably adapted. Foran in-plane field rotating counterclockwise, magnetic poles aregenerated at the inside end of each chevron element; next at the apex ofeach chevron element; and thereafter at the outside end of each elementof the propagation ring. Spurious domains, represented by circles D inFIG. 3, are either excluded by the outward progression of poles sogenerated in the elements of the ring 12 or moved outwardly from thearea encompassed by the ring as the number of spurious domainsincreases.

It is helpful to appreciate that high-speed operation is contemplated.Only domains moving in channels defined by the pattern of magneticallysoft elements experience field gradients resulting from the rotatinginplane field (see source 20 of FIG. 1). Spurious domains do notexperience such field gradients and are positioned mainly by thepressure of other domains. Spurious domains generated close to channelsalso ex perience a net repulsion force from domains moving about thechannels at high speeds. Only when a sufficient number of spuriousdomains press upon one another, causing all the available space to beclosely occupied, are spurious domains closely pressed into thepropagation channel in a manner to cause an occasional failure byinteraction or by the occupation of one space in the data stream by aspurious domain. Formation of .a propagation annulus about three domaindiameters away from the operative circuit takes ad-' vantage ofrepulsion forces between spurious and data domains to move the former tothe annulus for removal.

Sources 20 and 22 are under the control of a control "circuitrepresented by block 23 of FIG. 1 for activation and synchronization.

We have addressed ourselves mainly to the function of a propagation ringto move spurious domains outwardly during high-speed operation. The ringmayzbe used also to clear layer 1 l of domains which arise spuriouslyduring testing and characterization operations prior tohigh-speed'operation. In practice, single wall domains are maintained ata nominal operating size by a bias field supplied by a sourcerepresented by block 22 of FIG. 1 as is well known. A decrease inthemagnitude of the bias field causes domains to increase in sizeandfirrally to strip out. If, after testing, the bias field is lowered,all domains in layer 11 strip out and latch onto poles simultaneouslygenerated in the ring 12 by a counterclockwise rotating in-plane field.An increase in the in-plane field returns domains to an operating sizeto be removed, by the ring, from the operative part of layer 11. Somedomains may remain within propagation channels during such a clearingoperation. But these can be moved to an annihilator (not shown buttypically present in operative circuits) for elimination.

Two multiple element rings of the type described here may be arrangedconcentrically, a first to move domains from within, a second to movedomains to the areaencompassed within it. lf the second surrounds thefirst, all spurious domains are moved to a well-defined area between thetwo rings for annihilation. A double annulus arrangement of this type isparticularly suited also in conjunction with operative devices in whichthe in-plane field is reversed in orientation sequency (viz: fromcounterclockwise to clockwise) normally during operation. FIG. 1represents a second annulus of this type as a line designated 30.

Also, in practice, a propagation annulus with multiple elements as shownin FIG. 2 with apices aligned along a path defined by a closely coiledhelix of like elements rather than by closely spaced concentric circles.The helix geometry results in a total clearing of the propagationannulus. The circular geometry permits domains under some conditions tostrip out and almost close on themselves into a helical geometry leavingdomain tips which may give rise to spurious domains. Particularly at thehigh speeds contemplated, however, the domain generated by such tips arenegligible and the helix is employed to avoid a helical strip domainprimarily to approach an ideal condition where the propagation annuluscleans itself of domains constantly.

It is assumed that the pattern of elements which form the variouschannels of FIG. 1 are designed for a counterclockwise rotating in-planefield for consistency.

What has been described is considered merely illustrative of theprinciples of this invention. Therefore, various modifications inaccordance with those principles can be devised by those skilled in theart within the spirit and scope of this invention.

What is claimed is:

l. A magnetic arrangement comprising a layer of magnetic material inwhich single wall domains can be moved and a pattern of elements fordefining in said layer a first multistage propagation channel having anaxis, said elements having geometries and being disposed to effect a netmovement of domains only laterally with respect to said axis in responseto a cycle of a magnetic field'reorienting in the plane of said layer.

2. An arrangement in accordance with claim 1 also including a pattern ofelements for defining an additional multistage domain propagationchannel to said first side of said axis for the movement of domainstherein in response to said magnetic field.

wherein said axis is curved to encompass said additional channel. I

4. An arrangement in accordance with claim 3 wherein said axis closes-onitself to encompass said additional channel completely.

5. An arrangement in accordance with claim 4 wherein said elements ofsaid first channel comprise a fine-grained pattern of chevron elementsthe apices of which align with said axis.

6. An arrangement in accordance with claim 4 wherein said elements ofsaid first channel are spaced apart from said additional channel adistance equal of about three times the diameter of a domain moved insaid additional channel.

7. An arrangement in accordance with claim 4 also including a thirdpropagation channel defined along a circular axis encompassing saidfirst channel, said third channel including elements of a geometry andso disposed to move domains inwardly across said circular axis inresponse to said magnetic field.

jacent rings to move domains in a direction outwardly from said firstside in response to said reorienting magnetic field.

10. An arrangement in accordance with claim 9 also including means forproviding said reorienting magnetic field.

11. An arrangement in accordance with claim 9 also including means forproviding a bias field for maintaining domains at a nominal operatingsize in said layer.

1. A magnetic arrangement comprising a layer of magnetic material inwhich single wall domains can be moved and a pattern of elements fordefining in said layer a first multistage propagation channel having anaxis, said elements having geometries and being disposed to effect a netmovement of domains only laterally with respect to said axis in responseto a cycle of a magnetic field reorienting in the plane of said layer.2. An arrangement in accordance with claim 1 also including a pattern ofelements for defining an additional multistage domain propagationchannel to said first side of said axis for the movement of domainstherein in response to said magnetic field.
 3. An arrangement inaccordance with claim 2 wherein said axis is curved to encompass saidadditional channel.
 4. An arrangement in accordance with claim 3 whereinsaid axis closes on itself to encompass said additional channelcompletely.
 5. An arrangement in accordance with claim 4 wherein saidelements of said first channel comprise a fine-grained pattern ofchevron elements the apices of which align with said axis.
 6. Anarrangement in accordance with claim 4 wherein said elements of saidfirst channel are spaced apart from said additional channel a distanceequal of about three times the diameter of a domain moved in saidadditional channel.
 7. An arrangement in accordance with claim 4 alsoincluding a third propagation channel defined along a circular axisencompassing said first channel, said third channel including elementsof a geometry and so disposed to move domains inwardly across saidcircular axis in response to said magnetic field.
 8. An arrangement inaccordance with claim 5 wherein said elements of said first channelcomprise a plurality of chevron elements having their apices alignedalong a closed helical path generally coincident with said axis.
 9. Anarrangement in accordance with claim 5 wherein said elements of saidfirst channel comprise a plurality of concentric rings each comprising apattern of chevron elements the apices of which lie along the respectiverings forming curved chevron patterns, said elements being disposed withrespect to elements of adjacent rings to move domains in a directionoutwardly from said first side in response to said reorienting magneticfield.
 10. An arrangement in accordance with claim 9 also includingmeans for providing said reorienting magnetic field.
 11. An arrangementin accordance with claim 9 also including means for providing a biasfield for maintaining domains at a nominal operating size in said layer.